Developers are scrambling for the next Kendall Square. Where will it be?

The Boston Flower Exchange building and parking lot on Albany Street. John Tlumacki/Globe Staff/File/Globe Staff

From the Alewife section of Cambridge to the outer reaches of the Seaport District, from Union Square in Somerville to Barry’s Corner in Allston, developers all over Greater Boston are trying to build “the next Kendall Square.”

And it’s easy to see why.

The East Cambridge district is arguably the center of the nation’s biotechnology industry, as well as major outposts of innovative companies such as Apple, Boeing, and Google. That critical mass has other firms lining up to fill any space that becomes available, driving up rents higher than anywhere else on the East Coast, except for Manhattan.

“The most innovative square mile on the planet,” as Kendall Square boosters have been known to call it, is full to bursting. The vacancy rate for laboratory space is measured in tenths of a percent. That has developers as far away as Worcester seeking to capitalize on the overflow. They’re building lab space and life-science-oriented office buildings, promoting their locations as the “next Kendall Square.”

In their less-boosterish moments, however, most will acknowledge that nothing can ever match the status of Kendall. Its blend of tech, pharmaceutical, and science companies — big and small — combined with proximity to MIT, one of the world’s foremost research universities, would be impossible to replicate.

Harvard's School of Engineering and Applied Sciences is under construction on Western Avenue in Allston.Pat Greenhouse/Globe Staff/Globe Staff

“Kendall is the most scientifically influential square mile in the world, and they have a 40-year head start on everywhere else,” said Stephen Lynch, principal at King Street Properties, which has lab projects in the Alewife section of Cambridge and in Lexington, with another proposed in Allston. “That’s OK. There will be a lot more growth in life-science real estate here.”

But where?

Along with longtime suburban hubs in Lexington and Waltham, there are no fewer than 10 neighborhoods in Boston, Cambridge, and their immediate neighbors where builders are vying to create life-science districts.

Some, such as Alewife and the Seaport, have already built new lab buildings and attracted companies, including some that can’t find room in Kendall Square. Others, like the old Boston Flower Exchange site in the South End and a patch of South Boston around the MBTA’s Red Line’s Broadway station, are still in the planning stages. Still more, particularly Allston Landing near Harvard University’s new Science and Engineering Complex, are even further down the road, but have enormous potential.

“Maybe you can’t replace Kendall, but where else can you find lots of land adjacent to one of the world’s top universities?” said Brendan Carroll, director of intelligence at the real estate firm Perry. “Oh, right. Just across the river.”

Innovation Square in Boston’s Seaport is under development.Pat Greenhouse/Globe Staff/Globe Staff

It’s not likely all of these places will succeed, said Jonathan Davis, whose firm, Davis Cos., has built two lab buildings in Alewife and controls another 8 acres of older industrial property nearby that it plans to develop. It’s hard to create a cluster from a vacant tract, he said, and certain places just have built-in advantages, like being close to top hospitals and universities.

“It’s going to be a question of how many of these clusters are required, and where people are going to go,” Davis said. “You have to have some critical mass.”

Even more than some industries, life-sciences companies tend to group together, real estate experts say. That helps attract workers and fuels the interplay between small startups working on experimental drugs and the pharma giants that might acquire the up-and-comers. It also can give companies confidence — in a boom-and-bust industry — that should they need to grow or downsize quickly, they’ll have options nearby.

“Most companies don’t want to be a pioneer,” said Mark Winters, executive managing director at the real estate firm Newmark Knight Frank, who specializes in life-science deals. “That’s where the cluster comes in.”

Among his clients, Winters said, the Seaport, Fenway, and the eastern end of Watertown along Arsenal Street are emerging as the most popular destinations, after Kendall Square and Alewife. Most important to companies, Winters and other specialists say, is to locate where they can recruit the workers they need to grow. Even if it means paying a little more for a lease.

“It’s not just about cheap space,” said Brian Dacey, a veteran real estate executive who is president of the Cambridge Innovation Center. “It’s about being around like-minded people, money, ideas, and talent.”

Construction continues near Alewife. Pat Greenhouse/Globe Staff/Globe Staff

That has long been the argument for being in Kendall Square.

Despite Kendall’s astronomically high rents, companies compete to lease rare blocks of space there, and several major projects in the works — including MIT’s line of buildings along Main Street and the massive Cambridge Crossing just north of Kendall — are filling up fast. Large companies will pay top dollar to be close to the science spinning out of MIT and the neighborhood’s array of small drug and tech startups, said Robert Urban, the former global head of Johnson & Johnson Innovation in Kendall Square.

And Cambridge city officials and the district’s developers have been smart to set aside room for startups in new buildings, despite the blue-chip boom.

“The giants want to be among the innovators,” Urban said. “It’s a food chain. The plankton has to exist or the whales don’t exist, either.”

That mix, that food chain, is a big part of what makes Kendall Square Kendall Square, Urban said — and it’s hard to re-create somewhere else. But maybe each cluster doesn’t have to stand on its own.

Some of its backers envision Kendall Square evolving as the center of a regional cluster of life- sciences districts — in different parts of the city and suburbs — ideally connected by a transit system that makes it easy for people and their ideas to mingle, much as they do in Kendall Square today. The 4.7-mile extension of the Green Line through Somerville and Medford could help.

C.A. Webb, president of the Kendall Square Association, points to Silicon Valley as a kind of model. It’s a formless swath of suburban San Francisco, with no distinct boundaries. But it’s known worldwide as the home of the tech industry.

“I don’t know if Kendall will become that kind of broad moniker,” Webb said. “But it would be very exciting if the whole region became known as Kendall Square. We shall see.”